The present invention relates to a paper feed mechanism for a printer or the like for feeding paper which is used as a printing medium for the printer.
An example of a prior art paper feed mechanism for a printer or the like for feeding paper at a predetermined speed is a pin-tractor type mechanism such as shown in FIG. 1. This pin-tractor type mechanism comprises a drive pulley 11, a driven pulley 21, and a belt 4 trained about the two pulleys. Each of the pulleys 11, 21 includes pins 12 and 22 which engage with grooves 42 formed in the belt 4. Rotation of the drive pulley 11 causes rotation of the feed belt 4 in a predetermined direction. The drive pulley 11 is rotated by a drive shaft 1, and the driven pulley 21 is fitted on a support shaft 2 which supports the feed belt 4 with a predetermined tension. Provided at a predetermined interval on the outer surface of the feed belt 4 are pins 41. The pins 41 are engaged with perforations 91 formed linearly along both edges of printing paper 9 which often consists of several sheets stacked together. The paper 9 is therefore fed in the same direction as and in synchronism with the rotation of the feed belt 4.
A pressure plate 60 is provided over the paper 9 to ensure the engagement of the pins 41 with the perforation 91, i.e., to prevent disengagement of the pins 41 from the perforations 91 due, for example, to warping of the paper 9. By virtue of the pressure plate 60, the paper 9 is pressed against the feed belt 4 and is fed out while being pressed.
In the pin-tractor type feed mechanism described above, when the paper 9 is fed in synchronism with the rotation of the feed belt 4, a frictional force is created between the top surface of the paper and the pressure plate 60. The friction applies a reactive force on the top surface of the paper 9 in the direction opposite to the direction of feeding. When the speed of the feeding by the feed belt 4 is increased, the frictional force also is increased. Where stack of sheets of the paper 9 are fed, the top sheet of the paper 9 may have its perforations 91 disengaged from the pins 41, and may become incapable of being fed. This may result in damage to the perforations and faint printing on the paper.